DENIERS SAY:

The last 150 years of warming is just a natural recovery from the last ice age.

SCIENCE SAYS:

A planet doesn't "recover" from an ice age like we do from hypothermia. The Earth is warming up, and carbon pollution is to blame.

The “Little Ice Age,” the most recent cool period in the Earth’s history, may have been triggered by decades of intense volcanic activity. Scientists generally agree that the Little Ice Age ended in the late 19th century. So, could the warming we’re seeing now simply be a “recovery” after the Little Ice Age? No. Although the climate goes through cycles, there isn’t a normal recovery point. In other words, warming after an ice age isn’t like a human naturally recovering from hypothermia. Something has to force the climate to get warmer. In the early part of the 20th century, the Earth warmed because of less volcanic activity and more solar activity. But most of the warming from the mid-20th century onward has been due to carbon pollution from dirty fuels. And now, the planet is warmer than at any point in the last 1,000 years … meaning it’s warmer than well before the start of the Little Ice Age.

Additional info from Skeptical Science

The argument that we're simply "coming out of the Little Ice Age (LIA)" makes one of two assumptions:

1. The planet oscillates around some natural equilibrium temperature such that after it cools, it must warm to return to this temperature, and vice-versa.

2. Whatever caused the LIA cooling has reversed phase and is now causing global warming.

The first assumption demonstrates a lack of understanding regarding what causes planetary temperature changes. The second does not hold up under scrutiny of the empirical data.

Climate Change Causes

A long-term increase in the Earth's average temperature is caused by a change in the planetary energy balance (incoming vs. outgoing energy), also known as a "radiative forcing". If the amounts of incoming and outgoing energy are equal, the planet is in equilibrium and its temperature will not increase on average.

Note that over short periods of time, energy can be exchanged between the Earth's oceans and surface air through natural cycles such as the Pacific Decadal Oscillation, which can result in a short-term warming of the surface oceans and air at the expense of a cooling of the deeper oceans, or vice-versa. However, these cycles oscillate between positive and negative states, which over the long-term cancel each other out and do not cause significant temperature trends. These oscillations neither create nor retain heat; they simply move it around and thus physically cannot cause global warming or cooling. Further, if these cycles were causing the surface to warm, they would be causing the oceans to cool, which is the opposite of what we observe.

There are many different factors which can cause a planetary energy imbalance. Some of the most common examples are changes in solar activity, atmospheric greenhouse gases, volcanic activity, the Earth's overall reflectivity, and variations in the Earth's orbit around the Sun (also known as "Milankovitch cycles"). However, the key point is that the planet will not warm or cool over the long term unless there is a radiative forcing causing a planetary energy imbalance. Thus, the planet will not warm simply because it had previously cooled, and the notion that the planet is just "recovering" from the LIA makes no physical sense.